Polycystic Ovarian Syndrome (PCOS), a common cause of female infertility, is in many cases associated with insulin resistance. It is often treated by In Vitro Fertilization (IVF), but at IVF, these patients frequently have poor success, because of the effects of hyperinsulinemia on oocyte quality and successful implantation. If so, metformin use at IVF in PCOS patients will improve outcome, with a reduced risk of multiple pregnancy, and will also decrease the costs associated with this reproductive technology. As part of the University of Vermont Reproductive Medicine Network clinical site application, this concept protocol hypothesizes that in PCOS patients, the addition of metformin to the process of IVF will improve oocyte maturity, fertilization rates, implantation and pregnancy rates, and after pregnancy is established, continued metformin use will reduce the rate of embryonic loss, as well as adverse obstetric outcomes later in gestation. To address this issue, this application proposes a 500 subject multicenter, three arm, and randomized, blinded clinical trial, giving metformin both for 3 months prior and during the IVF cycle, and assessing oocyte and embryo quality. Further, the proposal continues the metformin or placebo through the first 12 weeks of gestation to assess the potential beneficial effect reducing embryonic loss. If this hypothesis is proven true, metformin administration at IVF would represent a novel and inexpensive way of optimizing IVF cycles in PCOS patients, allowing for a reduction in costs and number of embryos transferred, thus decreasing multiple pregnancy rates, while increasing the success of this procedure The strength of this concept protocol, combined with the inherent strengths of the reproductive medicine endeavor at the University of Vermont, as outlined in this application, illustrate the suitability of this institution as a clinical site for the Reproductive Medicine Network. [unreadable] [unreadable] [unreadable]